The present invention relates to a paper feeder for a printer, particularly to a paper feeder in which a stage of a paper tray on which sheets of paper are stacked up is moved toward a paper feeding means such as paper feeding rollers to feed the sheets of paper one by one to the printer.
FIG. 1 is a schematic diagram illustrating a side view of a conventional paper feeder for a printer, which was disclosed in the Published Unexamined Japanese Utility Model Application No. 59625/1987. Shown in FIG. 1 are a paper tray 1, a stage plate 2 of the paper tray 1, on which sheets of papers 4 are stacked up, the stage 2 being swingable about one end thereof as a fulcrum 3, a mounting portion 5 on which the paper tray 1 is mounted, a motor 6, an arm wheel 7 coupled to the motor 6, a paper feeding roller 8, a pair of paper conveyance rollers 9a and 9b, a pair of paper guides 10a and 10b, an actuator 11, and a photocoupler sensor 12 which act as means for detecting the height of the paper stacked up on the stage 2. The other free end of the stage 2 is urged upwardly by the tip 7a of the arm wheel 7 as indicated by an arrow in FIG. 1. When the uppermost one of the sheets of paper 4 on the stage 2 has then reached such a height as to come into contact with the paper feeding roller 8, the actuator 11 causes the photocoupler sensor 12 to stop the rotation of the arm wheel 7. Then, the paper feeding roller 8 rotates to feed the uppermost paper 4 so that the paper is conveyed along the paper guides 10a and 10b by the conveying rollers 9a and 9b.
The above described conventional paper feeder is disadvantageous in that the contact pressure between the paper feeding roller 8 and the paper 4 changes greatly due to the difference in the position of the paper detected by the photocoupler 12, as a result of which the sheets of paper cannot be fed to the printer stably. Further, since the contact pressure is about 200g, relatively high rotation torque is required to the arm wheel 7. This results in another drawback that it is necessary to employ an expensive motor having a speed reducer or the like as the motor 6 resulting in increasing the manufacturing cost of the paper feeder.